70 Composition of the Atmosphere 



berg. This apparatus is essentially on the Pettenkofer-Voit principle, 

 in that a current of fresh air constantly passes through the chamber. 

 The air leaving the apparatus is analyzed, the change in composition 

 being assumed to have resulted from the metabolic activity of the subject 

 inside the chamber. In his modification of the Pettenkofer-Voit appara- 

 tus, Jaquet has included the determination of the oxygen in the out- 

 going air-current, thus obtaining data regarding the amount of oxygen 

 used, as well as the carbon dioxide produced. With a large ventilation 

 the oxygen deficit may be very small in amount; conversely, the smaller 

 the ventilation, the larger will be the deficit. Unfortunately, most work- 

 ers with this apparatus, although recognizing the fact that the oxygen 

 deficit should be large rather than small, in practice frequently do not 

 heed it and many experiments have been reported in which it is but 0.50 

 per cent. Under these conditions, therefore, it can be easily seen that an 

 error in assuming the oxygen content of the incoming air may be of con- 

 siderable moment, for each 0.01 variation may make a difference of 2 per 

 cent in the determination of the oxygen absorbed. It might further be 

 said at this point, although it is not necessarily germane to this discussion, 

 that the small oxygen deficit so commonly used by workers with the 

 Jaquet apparatus is likewise enormously affected by analytical errors in 

 determining the oxygen in the out coming air. The Jaquet system is 

 simple, and has many advantages in its favor, but in using it an exact 

 knowledge of the composition of the air entering as well as of that leav- 

 ing the chamber is of fundamental importance. 



A knowledge of the exact oxygen content of the air inside the respira- 

 tion chamber is also of great importance in using the Regnault-Reiset type 

 of respiration apparatus. For example, assuming that the air in a chamber 

 containing 1000 liters has an oxygen percentage of 20.93, the oxygen con- 

 tent would be approximately 209.3 liters. An error of 0.1 per cent in the 

 determination of the oxygen would therefore result in an error of prac- 

 tically 1 liter in the total amount of oxygen residual in the chamber, so 

 that with an oxygen consumption of approximately 15 liters per hour, 

 the error in the determination of the total oxygen consumption might 

 easily amount to one-fifteenth, or approximately 6 per cent. 



One of the most important uses of the determination of the oxygen 

 content of the air in the chamber, however, is not so much to obtain an 

 exact knowledge of the amount of oxygen present as to indicate in an 

 elaborate and complicated apparatus the presence of a leakage of air into 

 or out of the system. This point was brought out in a former publica- 

 tion. 1 In a closed-chamber apparatus, it is obvious that with an initial 

 volume of 1000 liters of air there can be no change in the nitrogen content 

 by virtue of metabolic processes, 2 so that from hour to hour it should re- 



1 Atwater and Benedict, Carnegie Institution of Washington, Publication No. 42, 

 1905, p. 93. 



2 Krogh, Skandinavisches Archiv fur Physiologie, 1906, 18, p. 364. 



